1. Field of the Invention
The present invention is related to an optoelectronic device, especially related to an optoelectronic device having a multi-layer structure of epi-stacked structure for the enhancement of optoelectronic efficiency.
2. Description of the Prior Art
The crystal property of GaN compound needs to be improved for providing a solution on the issue of lattice matching between sapphire and GaN in an active layer. In U.S. Pat. No. 5,122,845, shown in FIG. 1, an AlN-based buffer layer 101 is formed between a substrate 100 and GaN compound layer 102, which is microcrystal or polycrystal to improve crystal mismatching between the substrate 100 and the GaN compound layer 102. In U.S. Pat. No. 5,290,393, shown in FIG. 2, an optoelectronic device is a GaN-based compound semiconductor layer 202, such as GaxAl1-xN (0<x≦1). However, during the formation of a compound semiconductor layer 202 on a substrate 200 by epi-growth, the lattice structure on the surface of the substrate 200 may influence the quality of a sapphire device. Thus, a buffer layer 201, such as GaxAl1-xN, is between the substrate 200 and the compound semiconductor layer 202 to improve lattice mismatching. Furthermore, in U.S. Pat. No. 5,929,466 or 5,909,040, shown in FIG. 3, an AlN layer 301 as a first buffer layer is formed on a substrate 300, an InN layer 302 as a second buffer layer is on the AlN layer 301, which may improve lattice mismatching near the substrate 300. However, the optoelectronic efficiency is restricted by the methods aforementioned. Thus, the present invention provides an optoelectronic device which includes a buffer layer with easily-growing II/V group compound layer associated with uneven surface of an active layer. Thus, the light brightness of the optoelectronic device is improved.